This invention pertains to chemical collectors and their use in the recovery of minerals by froth flotation.
Flotation is a process of treating a mixture of finely divided mineral solids, e.g., pulverulent ore, which are suspended in a liquid under process conditions such that a portion of the solids is separated from other finely divided mineral solids, e.g., silica, siliceous gangue, clays and other like materials present in the ore. The flotation process comprises introducing a gas (or providing a gas in situ) in the liquid to produce a frothy mass containing certain of the solids on the top of the liquid, and leaving suspended (unfrothed) other solid components of the ore. Flotation is based on the principle that introducing a gas into a liquid containing solid particles of different materials suspended therein causes adherence of some gas to certain suspended solids and not to others, and makes the particles having the gas adhered thereto lighter than the liquid. Accordingly, these particles rise to the top of the liquid to form a froth.
The minerals and their associated gangue which are treated by froth flotation generally do not possess sufficient hydrophobicity or hydrophilicity to allow adequate separation. Therefore, various chemical reagents, "collectors," are often employed in froth flotation to create or enhance the properties necessary to allow separation. Collectors are used to enhance the hydrophobicity and thus the floatability of different mineral values. Collectors must have the ability to (1) attach to the desired mineral species to the relative exclusion of other species present; (2) maintain the attachment in the turbulence or shear associated with froth flotation; and (3) render the desired mineral species sufficiently hydrophobic to permit the required degree of separation.
U.S. Pat. No. 5,173,176 generally discloses the techniques and problems associated with froth flotation and specifically discloses a process for recovering oxide minerals by froth flotation in the presence of a chemical collector. The collector is taught to be a dialkylated aryl sulfonic acid, such as, di(dodecyl)benzene sulfonic acid or a salt thereof. Preferred dialkylated aryl sulfonic acids are disclosed to contain one C.sub.1-3 alkyl substituent and one C.sub.10-24 alkyl substituent. Examples of this preferred type of collector include hexadecylcumene monosulfonic acid and octadecylcumene monosulfonic acid.
Dialkylated aryl sulfonic acids and their salts can be obtained commercially. Commercial samples are known to be prepared by traditional Friedel-Crafts or liquid acid technologies. For example, it is known to dialkylate benzene with an alkylating agent, such as an olefin, in the presence of a Friedel-Crafts reagent, such as aluminum chloride, or a liquid acid, such as phosphoric acid. The resulting dialkylated benzene can then be sulfonated with traditional sulfonating reagents, such as sulfur trioxide or sulfuric acid, to yield the corresponding dialkylbenzene monosulfonic acid. Disadvantageously, the alkylation step produces a mixture of ortho and para, and to a lesser extent meta, dialkylated isomers. Additionally, the alkyl moiety can be attached to the phenyl ring at a variety of isomeric positions along the alkyl chain. For example, in 1,4-dioctylbenzene the octyl moiety can be attached at the 2-, 3- or 4-position along the chain. Consequently, dialkylated aryl monosulfonates which are produced using traditional Friedel-Crafts or liquid acid catalysts exist as mixtures of many isomers. U.S. Pat. No. 5,173,176 is silent with regard to distinguishing the individual efficiency of each of these isomers in ore flotation applications.
U.S. Pat. No. 4,301,317 and European patent publication no. 0,469,940 teach the monoalkylation of benzene with long chain olefins typically having from 6 to 20 carbon atoms in the presence of dealuminated acid mordenite catalysts. It is taught that a mixture of phenylalkanes enriched in the 2- and 3-phenylalkane isomers is produced. These patent documents also teach the sulfonation of the phenylalkane mixture to the corresponding phenylalkane sulfonates, but are silent with respect to dialkylation and the isomer distribution obtained therefrom.
U.S. Pat. No. 5,026,933 discloses a process wherein a lower olefin, such as propylene, is oligomerized to a mixture of substantially linear C.sub.10+ olefins. Thereafter, it is taught that benzene can be alkylated with the linear C.sub.10+ olefins in the presence of dealuminated acid mordenite to yield linear phenylalkanes enriched in the 2-phenylalkane isomer. The phenylalkanes are taught to be sulfonated with fuming sulfuric acid to the corresponding alkylbenzene sulfonates. This patent is silent with respect to dialkylation and the isomer distribution obtained therefrom.
U.S. Pat. No. 5,004,841 discloses the alkylation of benzene with an olefin having preferably up to eight carbon atoms to form dialkylated benzene enriched in the para isomer. The catalyst is taught to be a dealuminated acid mordenite which is prepared by heating an acid mordenite having a silica/alumina molar ratio less than 40/1 and a Symmetry Index, as determined by X-ray diffraction, between about 0.5 and 1.0, and thereafter treating the heated mordenite with strong acid so as to prepare the dealuminated acid mordenite catalyst characterized by a silica/alumina molar ratio greater than 50/1 and a Symmetry Index of at least about 1.0. This patent is silent with respect to alkylation by olefins having more than eight carbon atoms, is silent with respect to phenylalkane isomer distributions, and is silent with respect to sulfonation.
It would be beneficial to know which of the many isomers of the dialkylated aryl monosulfonates taught in U.S. Pat. No. 5,173,176 are the most efficient collectors for ore flotation applications. Selective use of the most efficient collectors would maximize the productivity of ore flotation processes.